The invention relates to improvements in bookbinding methods and apparatus. More particularly the invention relates to improvements in methods of and in apparatus for assembling predetermined numbers of signatures into books, magazines, pamphlets and like printed products wherein the signatures are held together by several rows of stitches.
European patent application Ser. No. 0 295 220 of Meratti et. al. (published Dec. 14, 1988) discloses a bookbinding method according to which the signatures of a stack are connected to each other by two rows of stitches including a row of plain stitches and a row of looped stitches. A blade is employed to sever the thread at the row of plain stitches while the thread is under tension due to forward movement of the stacks along their path. Such severing operation is preceded by extraction of thread from the interior of the signature through that hole in the fold which is adjacent the row of looped stitches and by cutting of the extracted thread. When the severing operation is completed, the stack of signatures is free to breathe (i.e., to expand) which causes a loosening of the rows of stitches. Furthermore the method of Meratti et. al. produces relatively long tails constituted by portions of thread at the severing locations; such elongated thread portions can interfere with further processing of the stacks of signatures.
Another drawback of the method of Meratti et. al. is that the signatures are likely to be damaged in the regions around the holes in their folds. This is due to extraction of thread from the signatures while the signatures are maintained in tightly compacted condition. Furthermore, it is rather difficult to properly and reliably engage the thread because such thread forms a relatively small loop.